Following rapid development of the IT (Information Technology) industry, a recent electronic device, in particular, a semiconductor device, a color filter or a TFT (Thin Film Transistor) device for a LCD (Liquid Crystal Display) monitor, or the like, is required to have a finer structure. One of techniques supporting fine process technology for such a finer structure is a lithography technique using a photo mask called a transfer mask. In the lithography technique, a silicon wafer with a resist film is exposed through the transfer mask to an electromagnetic wave emitted from an exposure light source so that a fine pattern is formed on the silicon wafer. Generally, the transfer mask is manufactured by preparing a mask blank comprising a light transmitting substrate and a light shielding film formed thereon and then forming, as a pattern of the transfer mask, an original pattern on the mask blank by the use of the lithography technique. If foreign matters such as particles are present on a surface of the mask blank, this may result in occurrence of a defect of the pattern formed on the transfer mask. Therefore, the mask blank must be stored in a clean environment so that no foreign matters are adhered or attached to the surface of the mask blank.
For example, as a conventional container for housing, storing, and carrying such mask blank, a mask carrying case is disclosed in JP-B-H01-39653 (Patent Document 1). Specifically, the conventional container for housing and storing a mask blank comprises an inner case called a carrier, an outer case (container body), and a cap. Generally, several to several tens of mask blanks are held in the inner case in parallel to one another. The inner case with the mask blanks held therein is received in the outer case. Then, the cap is put on the outer case. In this manner, the mask blanks are housed in the container.
FIGS. 11 to 13 show a container similar in structure to that disclosed in Patent Document 1. FIG. 11 is a perspective view showing a cap of the container. FIG. 12 is a perspective view showing a state where a mask blank is housed in an inner case. FIG. 13 is a perspective view of a container body (outer case) of the container.
The container comprises an inner case 2 for housing a mask blank 1, a container body 3 for housing the inner case 2, and a cap 4 put on an opening side of the container body 3.
The inner case 2 is provided with a plurality of pairs of grooves 21 and 22 formed at a predetermined interval on a pair of opposite inner surfaces opposite to each other in one direction, respectively. The grooves 21 and 22 extend from an opening side (upper side) towards a bottom side (lower side) of the inner case 2. Opening windows (not shown) are formed at bottom portions of the grooves 21 and 22 on the bottom side of the inner case 2. An opening portion 27 is formed on a bottom surface of the inner case 2. Furthermore, a substrate supporting portion 26 is formed on the bottom side of the inner case 2 and supports a lower end face of the mask blank 1 (FIG. 12). On a pair of opposite outer surfaces of the inner case 2 opposite to each other in the other direction perpendicular to the one direction, recessed surfaces 28 and 29 for fixing the inner case 2 housed in the container body 5 extend from the bottom side to an intermediate position towards the opening side. When a plurality of mask blanks 1 are inserted into the inner case 2 along the grooves 21 and 22, the mask blanks 1 stand in parallel to one another at the predetermined interval.
The container body 3 is provided with protruding portions 31 and 32 which are formed on a pair of opposite inner surfaces opposite to each other in the other direction and which are adapted to be brought into contact with the recessed surfaces 28 and 29 of the inner case 2. The protruding portions 31 and 32 have bottom portions connected to a bottom surface of the container body 3 (FIG. 13). On a pair of opposite outer surfaces opposite to each other in the one direction, projecting portions 33 and 34 are formed on the opening side, respectively. The projecting portions 33 and 34 have projecting surfaces substantially flush with an outer peripheral surface 36 formed adjacent to and slightly below an opening edge 35 of the container body 3.
The cap 4 has engaging portions 41 and 42 extending upward from the center of a pair of opposite lower edges 47 (i.e., opening-side edges to be fitted to the container body 3, turned upside in FIG. 11) opposite to each other in the one direction, and a pair of recessed portions 43 and 44 formed on the engaging portions 41 and 42, respectively. With this structure, when the cap 4 is put on the container body 3, the recessed portions 43 and 44 are engaged with the projecting portions 33 and 34 of the container body 3, respectively, so that the cap 4 and the container body 3 are fixed to each other. The cap 4 is further provided with stoppers 45 and 46 which are formed on a pair of opposite inner surfaces opposite to each other in the other direction, respectively, and which are faced to each other. The stoppers 45 and 46 are adapted to be brought into contact with an upper end face 25 (i.e., opening-side edges) of the inner case 2 to support and fix the inner case 2 in a vertical direction.